Method of making a cylinder boss



June 1 1965 A.J.wr:A1-HERHEAD, JR 3,186,368

METHOD OF MAKING A CYLINDER BOSS Original Filed March 8, 1962 2 Sheets-Sheet 2 /l/ INVENTOR.

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United States Patent O 3,186,368 METHOD OF MAKING A CYLINDER BOSS Albert I. Weatherhead, Jr., Shaker Heights, Ohio, assigner t The Weatherhead Company, Cleveland, Ohio, a corporation of Ohio Original application Mar. 8, 1962, Sel'. No. 178,337, now Patent No. 3,152,718, dated Oct. 13, 1964. Divided and this application May 5, 1964, Ser. No. 364,998 11 Claims. (Cl. 113-121) This application is a division of my copending application, Serial No. 178,337, led March 8, 1962, which issued as U.S. Patent No. 3,152,718, dated October 13, 1964.

This invention relates generally .to metal containers for compressed or liquied gases and more particularly to portable cylinders made from sheet metal for storing and dispensing liquiied petroleum gas.

Containers for transporting and storing compressed gases, particularly liquified petroleum gas, are generally formed as an elongated cylinder having substantially hemispherical caps on each end. of `the cylindrical center section. The top end cap is formed with a raised boss on its central portion which is provided with a threaded opening to receive the valve for controlling the flow of gas from the tank. In addition, this boss has a cylindrical outer wall portion which is threaded to receive a protective cap or guard which ts over the valve in order to prevent damage in transit. In addition to this, the boss generally has an annular portion which is stamped with the cylinder weight, and the manufacturers name and serial number, which are required by I.C.C. regulations to identify the particular cylinder and its manufacturer.

I-Ieretofore, pressure cylinders have generally been made in two different ways. In one of these methods, the threaded end opening is hot spun integrally with the cylindrical body which is fabricated by piercing and drawing from a steel billet. With this method the cylinder boss portion can be made with extremely thick walls to give the necessary strength after the boss has been machined to provide the internal opening and interior and external threads. This method, which is generally used on extremely high pressure, thick walled heavy cylinders requires relatively complex and expensive equipment and therefore has been replaced for liquified petroleum gas cylinders by methods of fabricating the cylinder body and end caps from sheet steel. However, it has not been previously possible with drawn steel and caps to provide sufficiently thick material at the cylinder boss location to allow the cutting of the threads and the stamping of the necessary information on the boss while still maintaining the wall thickness required for strength and to comply with applicable regulations. Therefore, the end `cap has generally been formed as a hemisphere having a centrally located opening about which is welded a cylinder boss assembly which is either machined from a heavier piece of metal or fabricated from a plurality of steel stampings.

While this method has produced a cylinder boss having the necessary burst strength and other properties necessary to pass safety tests, it represents an undesirably complex manufacturing process to produce the separate cylinder boss structure and weld it in place on the formed end cap.

It is therefore a principal object of the present invention to provide an end cap for a relatively light weight pressurized gas cylinder in which the complete cylinder boss structure is integral with an end cap and formed from a single metal blank.

It is another object of this invention to provide a novel and improved meth-od of making pressurized gas cylinders.

It is another object of this invention to provide a pres- 3,186,368 Patented June 1, 1965 ICC surized gas cylinder in which the end cap and cylinder boss are formed from a single blank of drawn steel in which the metal around a raised cylinder boss has a thickness at least as great as that of the remainder of the end wall and is provided with machined threads on its outer periphery and central aperture .to receive the guard cap and valve, respectively.

It is another object of this invention -to provide a one piece pressure gas cylinder end cap and cylinder boss which is at least as strong as end caps having welded cylinder boss inserts for the guard and valve receiving portions.

It is another object of this invention to provide a novel and improved seam for joining together adjacentportion of metal which provides maximum strength and freedom from leakage.

It is another object of this invention to provide a method of forming lapped joints between adjacent portion of sheet metal using a c-ombination of resistance welding and copper brazing techniques.

It is still another object of this invention to provide a pressure cylinder for liquied petroleum gas which is simpler in construction and of lower cost in manufacture.

The foregoing` and additional features and advantages of this invention will readily become apparent to those skilled in the art from the following detailed description of the preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a longitudinal cross-sectional view of a pressurized gas cylinder according to the present invention;

FIGURE 2 is a cross-sectional view through the cylindrical center section of the tank .taken on line 2-2 of FIGURE l;

FIGURE 3 is an enlarged fragmentary cross-sectional view of the cylinder boss;

FIGURE 4 is a fragmentary sectional view of the seam taken on line 4--4 of FIGURE 1; and

FIGURES 5 through 10 are cross-sectional views of the top end cap -of the cylinder showing the successive drawing operations employed in forming the end cap and cylinder boss as an integral unit.

Referring now to the drawings inV greater detail, and more particularly to FIGURE 1, the pressure cylinder shown therein is formed completely from sheet steel and includes a cylindrical center section 10, a top cap 11, and a bottom cap 12. The bottom cap 12 is generally convex in shape and carries a foot ring 14 which is secured to the bottom cap 12 along a continuous welded joint 15. The foot ring 14 serves as a support for the cylinder to hold it in an upright position, and is formed by bending from a strip of steel and welding the ends together along a butt joint 16. The lower edge of foot ring 14 has an inwardly and upwardly turned rimmed portion 18 to give the necessary strength at this point.`

The cylindrical center section is formed by bending a sheet of steel into a cylindrical form and joining the Vvedges together along a longitudinal seam indicated at 20.

As shown in greater detail in FIGURES 2, 4 and 5, the longitudinal seam 20 is of the lapped type in which one edgehas a portion 21 which is offset by the thickness of the steel sheet toward the inside of the cylinder along the ine 22. The other edge 24 therefore makes abutting contact along the offset line 22 and over-lapping contact along the offset portion 21. At the ends of the longitudinal seam 20, .the offset portion 21 is cut away to form notched portions 25 so that the inner periphery of the cylindrical center section 10 is perfectly smooth at this point and the two edges make contact only along the offset line 22. Top cap 11 and bottom cap 12 have cylindrical portions 27 and 28, respectively, which fit Within 'annessa the cylindrical center section for a depth substantially equal `to that of the notched portion 25. The caps Il. and 12 are thus joined to the cylindrical center section 10 along continuous welds 3l and 32., respectively, and this weld is continued down toward along the offset edge 21 for a distance equal to the depth of the notched portion 25. Thus, the assembly of the center section I@ with the two end caps il and I2 produces a rigid and leak free cylinder.

A longitudinal seam 2t? is preferably formed by a combination of welding and brazing techniques. Although this seam could be formed with a continuous weld from end to end along the odset line 22, such a weld requires special holding fixtures because the localized heating of the metal would cause the formed cylindrical section to distort during welding and result in a non-cylindrical section which would prevent proper fitting of the end caps.

To overcome this problem, the longitudinal seam is formed by bending the metal blank until the edge 24 overlaps the Ioffset edge portion 2l and is in alignment with the offset line 22, after which the blank is held in this position by clamps at each end. The seam can then be secured in a strong, rigid, but not leak free manner by a member of spaced spot welds indicated at 34 in FIGURE l. The seam 26 is then finished and sealed by means of a brazing operation which provides a brazed joint for the full width of the longitudinal seam 2li and prevents any leakage at this point. This is done preferably by placing a thin strip or foil of copper or other suitable brazing material be-V tween the edge 24 and the offset portion ZI prior to the spot welding operation. This strip of brazing material is of the same Width as the finished joint and preferably has a thickness between L002 and .006 inch. The spot welding at the points 34 is done after the foil is in place and the application ofthe spot welding current creates an arc through the foil which results in a localized melting and physical displacement of the copper in the area between the electrodes. Thus the thin copper or brazing metal foil is substantially removed from the spot weld area to permit a direct steel to steel weld of high strength as if the copper were not present. The spot welds rigidly secure the edges of the seam together without further clamping and the center section is then placed in a furnace at a temperature high enough to melt the brazing metal and allow it to adhere to the joint edges and secure them together in a strong and leak-free manner. Alternatively, the brazing can be accomplished after spot welding by placing a bead of brazing metal along the joint between the edge 24 and the offset line Z2 so that when the center section is heated in a furnace, the brazing metal will flow into the space along the oset portion 21.

As shown in greater detail in FIGURE 3, the top cap 11 has a centrally located boss structure S which is formed integrally with the top cap. Top cap 11 is generally convex in'shape so that the wall portion 37 is curved to extend substantially normal to the longitudinal axis of the tank at a point adjacent the boss structure 36. Boss structure 36 includes a cylindrical outer wall portion 39 which merges into wall portion 37 at its lower edge 40 and into a flat annular top wall portion 42 at the upper edge 43. At its inner edge 45, a top wall portion 42 merges into an inner cylindrical wall section 46V kwhich* extends inward into the tank where it terminates at a lower edge 47.

The outer cylindrical wall portion 39 is formed with threads 49 which receive a protective cap 50 of the usual kind adapted to extend over and cover the tank outlet valve. The inner cylindrical wall portion 46 is likewise provided with tapered pipe threads 52 to receive the outlet valve 53 from which a dip tube 55 extends downward toward the center portion of the tank.

Since the threaded portions 49 and 52 have the threads formed directly into the wall of the top cap, the wall at lthese points must be at least as thickV as it is over the hemispherical portion 37 to give the tank the necessary burst strength. It is well known that when a flat blank is drawn into a cup the thickness of the sheet is thinned by the stretching that takes place over the face of the punch. This stretching and thinning of the wall is particularly pronounced in the drawing of hemispherical or conical cups, and the wall is thinned to the greatest extent at the center of the punch. Thus, if the top cap ill were drawn directly to the final shape the wall of the boss structure 36 would be considerably thinner than the outermost wall portions and would therefore be too thin to allow forming of the threads i9 and 52.

For the above reason, applicant employs the drawing process shown in FIGURES 5 through l0 to avoid this thinning and stretching of the metal'at the center of the blank. The blank is first cut to have an initial diameter approximately 25% greater than the finished diameter of the tank. This tlat blank is then given a first draw to the shape indicated in FIGURE 5 having convex center section 53 and a radially extending flange 59. The second operation shown in FIGURE 6 draws the radially outer portion of the center section 58 of FIGURE 6 inward toward the plane of radial flange 59 to give a structure having a conical wall 6l slopingupward from flange 59, which remains unchanged, to a cylindrical wall portion 62 which terminates in a attened top portion 63.

During the third, fourth and fifth operations shown in FIGURES 7, 8 and 9, respectively, the radial iiange 59 and the conical wall ell remain unchanged, as does the diameter of the cylindrical wall portion 62. ln the third operation shown in FGURE 7, the top portion is drawn inward in the center to form a shallow depression indicated at 65. At the same time, the top wall portion 63 is pressed downward to slightly thicken the cylindrical portion 62 and provide additional material for forming Y the depression 65 without substantially thinning the wall at that point. The fourth and fifth operations shown in FIGURES 8 and 9 show the depression 65 pressed progressively inward so that its depth is increased while its diameter decreases. The effect of this is to transfer some of the metal from the side Walls 66 of depression 65 upward into the horizontal top portion 63. As a result of 'this transfer, the thickness is reduced only in the center portion 68 of the depressi-on 65, and the thinning at this point is of lno consequence because center portion 68 is subsequently punched out to provide the necessary opening to receive the valve.

The final operations are indicated in FIGURE 10 where the radial ange 59 and conical wall 6l are drawn downward and inward to form the curved wall portion '71 and cylindrical portion 72 of the finished top cap. At the same time, the cylindrical portion 62 is reduced slightly in a sizing draw tothe proper diameter before the threads are formed, `and the centrally depressed portion e5 is struck from the undersidel to decrease the depth and thicken its side walls 66. After this has been done, the center portion o8 of the depression 65 is punched out and the top cap is ready for the threading operations.

Thepthreads 49 on the outer cylindrical wall 39 are preferably rolled to avoid removal of any metal at this point, while the'innerrthreaded portion 52 has the threads cut to form a tapered pipe thread to give a leak-free seal at the Valve. Since the cutting of the threads 52 decreases the wall thickness, and since the inner cylindrical portion te has its lower edge 47 unsupported, the effect of iiuid pressure within the cylinder is such as to causea reduction in diameter of the inner cylindrical wall portion 4o and thereby press the threads more tightly into engagement with the valve. Thus, this construction provides a pressure assisted seal at this point and any slight thinning of the wall 46 is not detrimental to the burst strength of the cylinder.

After the top cap 11 has been completely formed as *described above, it is pressed into the cylindrical center section l@ and is preferably formed to have a diameter such as to make this a relatively tight press fit. Subsequently, the bottom 'cap 12 is pressed into the other end of the cylindrical center section in a similar manner and the welding completed around the portions indicated at 31 and 32 to form a pressure tight cylinder.

While the preferred embodiment of the pressure cylinder and the preferred method of making it have been shown and described in considerable detail, it is understood that this invention is not, limited to` such forms and methods, and various modifications and rearrangements as will appear to those lskilled in the art may be made without departing from the scope ofthe invention as set forth in the following claims.

What is claimed is:

1. The method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a flat circular blank ofsheet metal to have a substantially hemispherical center section of a predetermined depth and a fiat radial "flange, drawing the radially outer portion of said Uhe'rnispherical section inward toward said radial fiange to form a conical portion from which projects a cylindrical outer boss wall and a flattened top wall parallel to said radial flange, the total depth of said conical portion and cylindrical outer boss wall being substantially equal to said predetermined depth, drawing the center portion of said attened top wall inward to form an inwardly projecting cup, piercing the bottom portion of said central cup, and finished drawing said radial flange to form a cylindrical section adapted to fit within a cylindrical tank section.

2. The method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a fiat circular blank of sheet metal to have a substantially hemispherical center section and a fiat radial flange, drawing the radially outer portion of said hemispherical section inward toward said radial ange to form a conical portion from which projects a cylindrical outer boss wall and a flattened top wall parallel to said radial fiange, drawing the center portion of said flattened top wall inward to form an inwardly projecting cup, upsetting said flattened outer Wall toward said radial flange and said conical section to increase the thickness of said cylindrical outer wall, upsetting said cup to decrease its depth to increase the thickness of the Walls thereof, piercing the bottom portion of said central cup, and finished drawing said radial fiange to form a cylindrical section adapted to fit within a cylindrical tank section.

3. The method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a flat circular blank of sheet metal rto have a substantially hemispherical center section and a fiat radial flange, drawing the radially outer portion of said hemispherical section inward toward said radial flange to form a conical portion from which projects a cylindrical outer boss wall and a flattened top wall parallel to said radial flange, drawing the center portion of said attened top wall inwardly to form an inwardly projecting cup in'at least two stages, each of said stages causing said cup to decrease in diameter and increase in depth toward said radial flange, upsetting said flattened outer wall toward said radial flange and said conical section Ito increase the thickness of said cylindrical outer wall, upsetting said cup to decrease its depth to increase the thickness of the Walls thereof, piercing the bottom portion of said central cup, and finished drawing said radial flange to form a cylindrical section adapted to fit within a cylindrical tank section.

4. The method of forming a cylinder boss on the end of a pressurized gas cylinder comprising the steps of drawing a blank of sheet metal to have a substantially hemispherical section drawing the radially outer portion of said hemispherical section to form a conical portion from which projects a cylindrical outer boss wall and a flattened top wall, drawing the center portion of said 6 flattened top wall inward to form an inwardly projecting cup in at least two stages, each of said stages causing said cup to decrease diameter and increase in depth, upsetting said fiattened outer wall toward said conical section to increase the thickness of said cylindrical outer Wall, upsetting said cup to decrease its depth to increase the thickness of the walls thereof, and piercing the bottorn portion of said central cup.

5. A method of forming an end cap and integral cylinder boss for a pressurized gas cylinder having a pair of radially spaced 'substantially parallel concentric cylindrical wall portions comprising the steps of drawing a fiat blank of sheet metal to form said pair of cylindrical Wall portions each having a length exceeding their finished length, and reducing the length of each cylindrical portion to increase the wall thickness thereof.

6. A method of forming an end cap and integral cylinder boss for a pressurized gas cylinder having a pair of radially spaced substantially parallel concentric cylindrical wall portions comprising the steps of drawing a at blank of sheet metal to form said pair of cylindrical wall portions each having a Alength exceeding its finished length, reducing the length of each of said cylindrical wall portions to increase the Wall thickness thereof, and thereafter rolling external threads on the outer of said cylindrical wall portions and cutting internal threads on the inner of said cylindrical wall portions.

7.- A method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a fiat blank of sheet metal to form a generally hemispheric portion, deforming said hemispheric portion forming a first substantially cylindrical wall portion closed at one end by a rst substantially fiat end wall and joining at its other end a conical portion, deforming said first end wall and said first cylindrical Wall portion reducing the length of said first cylindrical wall poi-:tion and forming a central recess in said first end wall having a second substantially cylindrical wall portion closed by a second end wall, subsequently deforming said second cylindrical wall portion increasing its length and decreasing its diameter, shortening said second wall portion without substantially changing its diameter thereby increasing its wall thickness, and cutting out said second end wall.

8. A method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a flat blank of sheet metal to form a generally hemispheric portion having a predetermined depth, deforming said hemispheric portion forming a first substantially cylindrical wall portion closed at one end by a first substantially flat end wall and joining at its other end a conical portion, said conical portion and first cylindrical wall portion having a total depth substantially equal to said predetermined depth, deforming said first end Wall and said first cylindrical wall portion reducing the length of said first :cylindrical wall portion Without substantially changing -its diameter and forming a -central recess in said first end wall having a second substantially cylindrical wall portion closed by a second end Wall, deforming said second cylindrical wall portion increasing its length and decreasing its diameter, shortening said second Wall portion without substantially changing its diameter thereby increasing its wall thickness, and cutting out said second end wall.

9. A method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a flat blank of sheet metal to form a generally hemispheric portion having a predetermined depth, deforming said hemispheric portion forming a first substantially cylindrical wall portion closed at one end by a first substantially fiat end wall and joining at its other end a conical portion, said conical portion and first cylindrical wall portion having a total depth substantially equal to said predetermined depth, deforming said first end wall and said first cylindrical wall portion adsense reducing the length of said first cylindrical wall portion without substantially changing its diameter and forming a central recess in said first end wall having a second substantially cylindrical wall portion closed by a second end wall, twice successively deforming said second cylindrical wall portion each time increasing its length and decreasing its diameter, andshontening said second wall portion without substantially changing its diameter thereby increasing its wall thickness, and cutting out said second end wall.

l0. A method of forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the Isteps of drawing a flat blank of sheet metal to form a generally hemispheric `portion having a predetermined depth, deforming said hemispheric portion forming a iirst substantially cylindrical wall portion closed at one end by a rst substantially at end wall and joining at its other end a conical portion, said conical portion and rstcylindrical Wall portion having a total depth substantially equal to said predetermined depth, deforrning said lirst end Wall and said first cylindrical Wall vportion reducing the length of said rst cylindrical wall portion without substantially changing its diameter and forming a central recess in said rst end wall having a second substantially cylindrical wall portion closed by a second end Wall, twice successively deforming said second cylindrical wall portion each time increasing its length and decreasing its diameter, and :shortening said second wall portion Without substantially changing its diameter thereby increasing its wall thickness, cutting out said second end wall, and forming threads on said first and secon wall portions.

11. A method ofV forming an end cap and integral cylinder boss for a pressurized gas cylinder comprising the steps of drawing a flat blank of Isheet metal to form a generally hemispheric portion having a predetermined depth while leaving a ilat radial flange therearound, deforming said hemispheric portion forming a rst substantially cylindrical wall portion closed at one end by a rst substantially at end wall and joining at its other end a conical portion, said conical portion and iirst cylindrical wall portion having a total depth substan- :tially equal to said predetermined depth, substantially deforming said rst end wall and said first cylindrical Wall portion reducing the length of said irst cylindrical wall portion Without substantially changing its diameter and forming a central recess in said -first end wall having a second `substantially cylindrical wall portion closed by a second end wall, subsequently twice deforming said second cylindrical Wall portion each time increasing its length and decreasing its diameter, shortening said second wall portion without substantially changing its diameter thereby increasing its Wall thickness and deforming said flange to a cylindrical shape, and thereafter cutting out Said second end wall.

References Cited by the Examiner UNITED STATES PATENTS 1,623,325 4/27 Wetmore 113--120 2,460,721 2/49 Thompson 29--539 2,880,686 4/59 Higgin 113-121 CHARLES W. LANHAM, Primary Examiner. e 

1. THE METHOD OF FORMING AN END CAP AND INTEGRAL CYLINDER BOSS FOR A PRESSURIZED GAS CYLINDER COMPRISING THE STEPS OF DRAWING A FLAT CIRCULAR BLANK OF SHEET METAL TO HAVE A SUBSTANTIALLY HEMISPHERICAL CENTER SECTION OF A PREDETERMINED DEPTH AND A FLAT RADIAL FLANGE, DRAWING THE RADIALLY OUTER PORTION OF SAID HEMISPHERICAL SECTION INWARD TOWARD SAID RADIAL FLANGE TO FORM A CONICAL PORTION FROM WHICH PROJECTS A CYLINDRICAL OUTER BOSS WALL AND A FLATTENED TOP WALL PARALLEL TO SAID RADIAL FLANGE, THE 